Flux Normalized to 4.04 AU
This is just the flux, adjusted to what it would be if the object was 4.04 AU away. To understand why we make this adjustment, imagine the headlights of a car approaching you at night. As the car gets closer and closer, the headlights look brighter and brighter to you. (This is explained by the inverse square law, which some of you may have studied.) The headlights themselves aren't changing, only their distance from you is changing. Similarly, since all the planets are moving, the flux we receive from them increases when they get closer, and decreases when they get farther away. Since we are interested in measuring true changes on the planet rather than just the changes due to distance, we sometimes adjust flux measurements to a common distance. When looking at Jupiter, we generally chose 4.04 AU because that is the closest Jupiter and Earth ever get.
Why don't we bother normalizing fluxes when we look at things very far away, like quasars? The reason is that they are so far away, the motions of the Earth and the quasar do not change the distance an appreciable amount even over many years. (The difference between something being 100,000,000,000,000,000,000 miles away and 100,000,000,000,100,000,000 miles away is not much!)